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Know the Science: 9 Questions To Help You Make Sense of Health Research

Know the Science: 9 Questions To Help You Make Sense of Health Research

4. Was the study a controlled clinical trial?

In a controlled clinical trial, investigators compare the effects of different treatments in groups of study participants who are as identical as possible in all other respects. For example, the outcomes in one group of participants who receive a new “experimental” treatment may be compared with the results of another group who received standard care, the “control group.” In effect the control group provides a “yardstick” for measuring the effects of the new treatment. In this case standard care is the “control” intervention.

Experimental group

Participants receive new treatment

Participants are observed, and results are recorded

Control group

Participants receive standard care

Participants are observed, and results are recorded

 
Design of a clinical trial in which a new treatment is compared to standard care.

What did the control group receive?

There are many kinds of control groups. Ideally, participants are assigned randomly to one of the study groups. This helps ensure that the two groups are as identical in all respects as possible except for the intervention they receive. Other kinds of control groups are sometimes used, but they have an increased likelihood that factors other than the intervention affected the results.

In placebo-controlled trials, the control group receives an inactive treatment designed to resemble the treatment being studied. One example of a placebo is a pill that is medically inert (inactive) but looks like the experimental medicine being studied. Another example, called a sham, is used when the treatment being studied is a procedure (e.g., acupuncture), not a product. A sham procedure is designed to simulate the active treatment but does not have any active treatment qualities. When possible, the “placebo” treatment and “experimental” active treatment are delivered in a “double-blind” fashion. That is, neither the investigator delivering the treatment nor the volunteer know what they are getting. This reduces the possibility the volunteers know what they are receiving.

Experimental group

Participants receive the actual treatment                        

Participants and investigators don't know which group each participant is in

Participants are observed, and results are recorded.

Control group

Participants receive an inactive (placebo or sham) treatment

Participants and investigators don't know which group each participant is in

Participants are observed, and results are recorded.

 
Design of a clinical trial using a placebo or sham treatment

This page last modified October 18, 2017